1. Field of the Invention
The present invention relates to a hose connecting structure which is suitable for use as a connecting structure and also relates to a method for forming a hose which is suitable for use as a connection when an air duct hose or a filler hose is connected with a mating member.
2. Description of the Related Art
In an air hose or a filler hose for an automobile, it has recently been practiced that a resin hose has been used instead of a rubber hose. When the resin hose is used as the air hose for the automobile, a negative pressure is applied on the air hose. It is better that the resin hose be made of a hard resin material in order to obtain resistance to the negative air pressure.
Conventionally, the air hose is incorporated into the automobile in the following manner. A mating pipe is inserted into a hose edge opening to connect the hose edge portion and the mating pipe. At that time, a clamp member clamps the hose edge portion and the mating pipe from an outer surface of the hose. This clamping prevents the hose edge portion from becoming lose. The hose edge portion is elastically adhered to the mating pipe so that the sealing is ensured.
Therefore, in this conventional connecting structure, the hose is required that has a hose edge portion that is closely adhered to the mating pipe. Although, when the hose is made of a hard resin material, the hose edge portion cannot be fully adhered to the mating pipe. Thus, in an air hose made of resin, it is desirable that the body portion of the hose is made of a hard resin material, and the edge portion of the hose is made of a soft resin material.
This is true for a filler hose or other hoses. For example, in the filler hose, it is considered that the body portion of the hose is made of a hard resin material in order to obtain oil resistance. It is further considered that the edge portion of the hose is made of a soft resin material.
Since the above resin hose requires a curved portion and a bellows portion, a blow molding method is preferably used to form the hose. In the blow molding method, a tubular or a bladder-like parison is expanded with air so that the parison closely contacts an inner surface of the mold. As a result, the parison is formed in the predetermined shape. Thus, the outer surface of the molded hose is accurately formed in the predetermined shape by the mold, but the inner surface of the molded hose is formed under a stress free condition. Therefore, the inner surface of the molded hose includes poor characteristics in its shape and dimensional accuracy.
In an air hose, a mating member such as a metal pipe is inserted into a hose edge opening, and a clamp member clamps the mating pipe and a hose edge portion. As a result, the hose edge portion is closely adhered to the mating member so that the sealing capacity is ensured. Therefore, when the hose includes poor characteristics in its shape of the inner surface of the hose edge opening and in its dimensional accuracy, i.e. the inner diameter and the thickness shows unevenness, the sealing capacity cannot be satisfactorily achieved.
In the resin hose formed by the blow molding method, the inner surface of the edge portion is polished so that the hose is formed in the predetermined shape and dimension.
When the polishing is performed, a hose forming step becomes complicated, and polishing powders remain at and around the polished portion. Therefore, a washing step is needed, and the hose forming step becomes even more complicated. As a result, the forming cost is increased.
The above problems are concerned with the resin hose which is formed by the blow molding method. When the hose edge portion is made of a soft resin material, the following problems arise.
There are few kinds of soft resin materials which ensure excellent sealing capacity. The selection of the soft resin materials is restricted by the need to satisfy other characteristics of the hose.
Oil resistance, for example, is required for the filler hose. Recently, regulation of oil penetration resistance has become strict, and the soft resin material cannot meet such demands.
The air hose loaded on a turbo engine car requires heat resistance. In this case, the soft resin material cannot meet such a demand.
The air hose or the filler hose for automobiles determine their shape with respect to its attachment space and the mating member.
When the above hoses are formed, the body portion of the hose is formed in the predetermined shape at the molding stage. Furthermore, each edge portion is preformed to connect to the mating member.
The length and the shape of the hose is different according to the type of the car, the shape and the kind of the mating member, or the attachment space. In this case, each hose must be formed in each different mold according to each different length and shape.
When the above hoses each require different molds, the cost for molds becomes expensive. Especially, when a few variety of hoses are formed, the forming cost is high.